This invention relates to fault detection apparatus for a motor driver interface circuit. Such an interface circuit is disclosed which connects motor power drive apparatus to a computer control and allows motor operation in a plurality of selectable modes. One of these modes is the control of a reversible DC motor with switching transistors in an H-bridge configuration. It is desired to include fault detection circuitry which monitors the switching transistors for short circuits to supply or ground voltage which might damage them. However, such monitoring should not produce a false fault signal due to noise or to the brief initial high current of a switching transistor when it is first turned on.